The primary objective of this project is to clarify the role of HTLV in the etiology of ATL. Secondary objectives center around determination of prevalence of infection in healthy donors, including clustering; determination of prevalence of infection in patients with ATL and in control groups of patients with other malignancies or autoimmune disorders; definition of risk factors through studies on the prevalence of infection in the first degree relatives of HTLV-positive cancer patients, longitudinal studies on infants of HTLV-positive and negative mothers, and studies on HLAtypes on lymphocytes of patients and controls; and determination of the mode of transmission of infection.